1. Field of the Invention
The present invention relates to a hologram recording medium, and in particular, to a hologram recording medium at which a hologram can be recorded by illumination of light.
2. Description of the Related Art
Conventionally, a rainbow hologram is added to a plastic card, such as a credit card, for purposes such as preventing counterfeiting, determining the genuineness of the card, and the like. A large amount of rainbow holograms are reproduced from an original plate, and therefore, all are the same image hologram. In recent years, a non-contact type IC card, in which a rainbow hologram is added thereto, such as, for example, “FeliCa®” developed by Sony Corporation, has become popular. Further, IC cards carrying an optical memory have also been proposed (Japanese Patent Application Laid-Open (JP-A) No. 2000-67203).
On the other hand, the present inventors have invented a recording/playback method in which a hologram is recorded on a recording medium in which a recording layer is formed on a non-optical-quality sheet member such as paper, a plastic card, or the like, and the recorded hologram is played-back at a high S/N ratio. Further, by applying this technology, the present applicant has developed a plastic card carrying a hologram memory, in order to strengthen the ID function and security function (http://www.fujixerox.co.jp/research/category/inbt/m_photonics/docs/holoca.pdf).
A hologram memory can carry arbitrary information, which can be written-in on demand. Therefore, biometric information for authentication, such as a fingerprint or an iris or the like, and digital information such as text or a video or the like, can be held as a hologram, and use as a multi-purpose memory is also anticipated. Further, as the form of the hologram to be written, there are image holograms which can be perceived by the naked eye, and Fourier-transformed holograms which are read mechanically by the illumination of laser light or the like.
However, a hologram recording medium, which is recordable but is not yet recorded (i.e., a raw hologram card), has the problem that the raw storability thereof is poor. Generally, a recording medium, on which information is recorded by the illumination of light, has poor raw storability. For example, a recording medium, which uses a photosensitive material such as a silver halide or the like, is stored in a state in which light is blocked therefrom. In the case of a raw hologram card, a clear image cannot be obtained by recording and playback of the hologram merely by storing the raw hologram card in a state of being shielded from light.